When the forces acting upon an object are balanced, the object will maintain its state of motion; that is, its velocity remains constant. If the forces are unbalanced, the object will either speed up or slow down. The reverse logic is also true: if an object has a constant velocity, then the forces are balanced. And if an object is speeding up or slowing down, the forces are unbalanced.
 

A table of velocity-time data portray how an object's velocity changes over time. The velocity includes both a value and a + or - sign. The +/- sign can be ingored as it only indicates the direction of movement. The direction that an object moves has no bearing on whether it is speeding up or slowing down. So the prudent student focuses on the absolute value of these velocity values. An inspection of the absolute values helps one to determine if the object is speeding up, slowing down or moving with a constant speed. 

An object that is speeding up would display velocities whose absolute values increase over time. Conversely, an object that is slowing down would display velocities whose absolute values decrease over time. For both of these instances, there would be an unbalanced force.

Finally, an object that is moving with a constant speed would display the same velocity value over the course of time. The forces acting upon such an object would be balanced.